This chapter reviews the relation between gesture and the natural signed languages of deaf communities. Signs were for centuries considered to be unanalyzable depictive gestures. Modern linguistic research has demonstrated that signs are composed of meaningless parts, equivalent to spoken language phonemes, that are combined to form meaningful signs. The chapter discusses a system called homesign used where a deaf child with hearing parents is not exposed to signed languages during language acquisition. Two ways in which gesture may become incorporated into a signed language through the historical process of grammaticalization are described. In the first, gestures are incorporated into a signed language as lexical signs, which go on to develop grammatical meaning. In the second, ways in which the sign is produced, its manner of movement, and certain facial displays, are incorporated not as lexical signs but as prosody or intonation, which may develop grammatical meaning. Finally, the chapter critically examines a new view in which certain signs are considered to be fusions of sign and gesture and proposes a cognitive linguistic analysis based in the theory of cognitive grammar.